An electronic device is known to have a substrate, on which an electronic part is arranged, and a heat sink. A radiation gel as a heat conductive material is filled between the substrate and the heat sink such that heat, which is generated by the electronic part, transfers to the heat sink through the radiation gel. Such an electronic device is described in, for example, Patent Document 1 (JP 2013-232654 A). The electronic device described in Patent Document 1 has a heat sink of which surface has a protruding portion and a recessed portion to suppress a transfer of the radiation gel such that an adhesive force of the radiation gel with respect to the heat sink is improved.
However, according to studies conducted by the inventor of the present disclosure, the transfer of the radiation gel cannot be suppressed sufficiently by such a simple structure of the surface having the protruding portion and the recessed portion.
For example, in the electronic device, the radiation gel may be expanded, a warpage may be caused in the substrate, and the heat sink may be expanded by a variation of temperature. As a result, a volume of the radiation gel occupying a clearance that is defined between the substrate and the heat sink may increase relatively. When the volume of the radiation gel increases relatively, the radiation gel is pressed by the substrate and the heat sink and spreads between the substrate and the heat sink.
In a case where a clearance defined between the substrate and the heat sink is non-uniform, when the volume of the radiation gel varies repeatedly, the radiation gel transfers between the protruding portion and the recessed portion of the heat sink and transfers away from a position where the radiation gel is arranged initially. Accordingly, the radiation gel transfers away from the electronic part that is subjected to a heat radiation, and a heat radiational efficiency of the electronic part may decrease.
Furthermore, the electronic device vibrates, for example, when being mounted in a vehicle. In this case, the transfer of the radiation gel may not be suppressed by the simple structure of the surface having the protruding portion and the recessed portion. Thus, the heat radiational efficiency of the electronic part may decrease.